/**
 * Copyright (C) 2009 SC 4ViewSoft SRL
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.achartengine.util;

import java.text.NumberFormat;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;

/**
 * Utility class for math operations.
 */
public class MathHelper {

	/** A value that is used a null value. */
	public static final double NULL_VALUE = Double.MAX_VALUE;
	
	
	/** A number formatter to be used to make sure we have a maximum number of fraction digits in the labels. */
	private static final NumberFormat FORMAT = NumberFormat.getNumberInstance();



	/**
	 * Computes a reasonable set of labels for a data interval and number of
	 * labels.
	 * 
	 * @param start start value
	 * @param end final value
	 * @param approxNumLabels desired number of labels
	 * @return collection containing {start value, end value, increment}
	 */
	public static List<Double> getLabels(MinMax span,
			final int approxNumLabels) {

		final double start = span.min.doubleValue();
		final double end = span.max.doubleValue();

		FORMAT.setMaximumFractionDigits(5);
		List<Double> labels = new ArrayList<Double>();
		double[] labelParams = computeLabels(start, end, approxNumLabels);
		// when the start > end the inc will be negative so it will still work
		int numLabels = 1 + (int) ((labelParams[1] - labelParams[0]) / labelParams[2]);
		// we want the range to be inclusive but we don't want to blow up when
		// looping for the case where the min and max are the same. So we loop
		// on
		// numLabels not on the values.
		for (int i = 0; i < numLabels; i++) {
			double z = labelParams[0] + i * labelParams[2];
			try {
				// this way, we avoid a label value like 0.4000000000000000001 instead of 0.4
				z = FORMAT.parse(FORMAT.format(z)).doubleValue();
			} catch (ParseException e) {
				// do nothing here
			}
			labels.add(z);
		}
		return labels;
	}

	/**
	 * Computes a reasonable number of labels for a data range.
	 * 
	 * @param start start value
	 * @param end final value
	 * @param approxNumLabels desired number of labels
	 * @return double[] array containing {start value, end value, increment}
	 */
	private static double[] computeLabels(final double start, final double end,
			final int approxNumLabels) {
		if (Math.abs(start - end) < 0.0000001f) {
			return new double[] { start, start, 0 };
		}
		double s = start;
		double e = end;
		boolean switched = false;
		if (s > e) {
			switched = true;
			double tmp = s;
			s = e;
			e = tmp;
		}
		double xStep = roundUp(Math.abs(s - e) / approxNumLabels);
		// Compute x starting point so it is a multiple of xStep.
		double xStart = xStep * Math.ceil(s / xStep);
		double xEnd = xStep * Math.floor(e / xStep);
		if (switched) {
			return new double[] { xEnd, xStart, -1.0 * xStep };
		}
		return new double[] { xStart, xEnd, xStep };
	}

	/**
	 * Given a number, round up to the nearest power of ten times 1, 2, or 5. The
	 * argument must be strictly positive.
	 */
	private static double roundUp(final double val) {
		int exponent = (int) Math.floor(Math.log10(val));
		double rval = val * Math.pow(10, -exponent);
		if (rval > 5.0) {
			rval = 10.0;
		} else if (rval > 2.0) {
			rval = 5.0;
		} else if (rval > 1.0) {
			rval = 2.0;
		}
		rval *= Math.pow(10, exponent);
		return rval;
	}

	public static class MinMax {

		public Number min;
		public Number max;

		public MinMax(List<List<Number>> all_series) {
			min = Double.POSITIVE_INFINITY;
			max = Double.NEGATIVE_INFINITY;
			// We iterate through all values of all series
			for (List<Number> series : all_series) {
				for (Number datum : series) {
					if (datum.doubleValue() < min.doubleValue())
						min = datum;

					// NOTE: This cannot be "else if"; it will fail with a single data point.
					if (datum.doubleValue() > max.doubleValue())
						max = datum;
				}
			}
		}

		public MinMax(Number min, Number max) {
			this.min = min;
			this.max = max;
		}

		public double getSpan() {
			return this.max.doubleValue() - this.min.doubleValue();
		}

		public static MinMax getAxisMinMax(List<List<Number>> all_series) {
			return new MinMax(all_series);
		}
	}
}
